The Big Programming Thread - Page 13

#include <stdio.h>
#include <math.h>

#define MAX 2000000

int primo(int);

int main(void)
{
	int i;
	long int suma = 17;
	
	for (i= 2; i * 6 + 1 < MAX; i++) {
		if (primo((i * 6) + 1) == 1)
			suma += ((i * 6) + 1);
	}
	
	for (i = 2; i * 6 - 1 < MAX; i++) {
		if (primo((i * 6) - 1) == 1)
			suma += ((i * 6) - 1);
	}
	
	printf("%d", suma);
	
	return 0;
}

int primo(int num)
{
	int i;
	float j;
	
	if (num % 2 == 0)
		return 0;
	
	if (num % 3 == 0)
		return 0;
	
	j = sqrt(num);
	
	for (i = 1; i * 6 + 1 <= j; i++) {
		if (num % (i * 6 + 1) == 0)
			return 0;
	}
	
	for (i = 1; i * 6 - 1 <= j; i++) {
		if (num % (i * 6 - 1) == 0)
			return 0;
	}
	
	return 1;
}

private void btnGo_Click(object sender, EventArgs e)
        {
            Stopwatch stopWatch = new Stopwatch();
            stopWatch.Start();
            Int64 Total = 0;
            List<int> list = new List<int>();
            Boolean isPrime = true;
            for (int i = 2; i <= 2000000; i++)
            {
                isPrime = true;
                foreach (int j in list)
                {
                    if (i % j == 0)
                    {
                        //Not a prime
                        isPrime = false;
                        break;
                    }
                   //****** Change Start ******
                   if (j > Math.Sqrt(i))
                        break;
                   //****** Change End ******
                } //j
                if (isPrime)
                {
                    Total += i;
                    list.Add(i);
                }
            } //i
            
            stopWatch.Stop();
            txtEuler.Text = Total.ToString() + " -- Time: " + stopWatch.Elapsed;
        }

    private void btnPrime10001_Click(object sender, EventArgs e)
        {
            Stopwatch stopWatch = new Stopwatch();
            stopWatch.Start();
            Int64 Total = 0;
            List<int> list = new List<int>();
            Boolean isPrime = true;
            int i = 2;
            while (list.Count() != 10001)
            {
                isPrime = true;
                foreach (int j in list)
                {
                    if (i % j == 0)
                    {
                        //Not a prime
                        isPrime = false;
                        break;
                    }
                    if (j > Math.Sqrt(i))
                    {
                        break;
                    }
                } //j
                if (isPrime)
                {
                   list.Add(i);
                }
                i++;
            } //i

            stopWatch.Stop();
            txtEuler.Text = list[10000].ToString() + " -- Time: " + stopWatch.Elapsed;
        }